The pressure in a hydraulic circuit of an automatic transmission can be regulated as a function of the need. Whereas the pressure level in the hydraulic circuit can be kept low for the supply of lubricant oil to the transmission parts, the pressure has to be markedly raised during the gear shifting operations, for example, in order to quickly fill up the shifting elements.
Normally, pressure regulators are used to actuate downstream slide valves that operate shifting elements in order to regulate the pressure in hydraulic circuits. In this process, the downstream slide valves are controlled within the pressure regulator by a proportional magnet including a magnet core, a magnet coil and a magnet armature. The proportional magnet regulates the coil current proportionally to the output quantity; the magnet armature and thus the downstream slide valve for clutch control are regulated in accordance with the coil current. The resultant characteristic magnetic-force current lines of the pressure regulator then serve as the basis for generating the characteristic lines needed to adjust the clutch in an electro-hydraulic control unit of automatic transmissions.
For example, German patent application DE 199 43 066 A1 describes an electromagnetically operated hydraulic proportional valve having a magnet part comprising an electrically controlled coil, a stationary core that protrudes into the coil interior and a sliding armature that is acted upon by the coil and that is coupled to a closing member, and operating channel as well as a valve seat which, while operationally connected to the closing member, regulates a pressure means connection between the operating channel and the return channel. Here, the closing member—at least in the area of its end facing the valve seat—has an essentially conical sealing element whose smaller front surface faces the valve seat, whereby the sealing element has at least one flow-separation edge on its end facing away from the valve seat.
This construction is intended to attain a stable behavior of the proportional valve vis-à-vis temperature effects and flow-related harmonic excitations. The pressure-flow characteristic lines of the proportional valve exhibit a more constant and steady curve in comparison to conventional pressure control valves since the sealing properties and the closing behavior of this proportional valve are improved.
Another proportional pressure control valve that is configured as a pilot valve having a pressure-reduction or pressure-maintenance function is described in German patent application DE 199 04 901 A1 of the applicant. It includes a valve housing with inlet and discharge openings, a control element, an armature rod and a proportional magnet that encompasses a magnet core, a magnet armature and a magnet coil, whereby the proportional magnet displays a virtually constant magnetic force in its operating range. In a holding position of the magnet armature, the smallest axial distance between the magnet armature and the magnet core is dimensioned in such a way that the magnetic force between these two components in the holding position is greater than the magnetic force in the operating range of the proportional magnet, whereby the magnet armature can be secured in this holding position by means of this magnetic force.
Furthermore, German patent application DE 100 34 959 A1 of the applicant describes a proportional pressure control valve having a valve part, with inlet and discharge openings and with at least one closing member that serves to control a diaphragm and one of the openings, as well as having a magnet part with a magnet core, a magnet coil and a sliding magnet armature. An actuation element interacts with the armature and it actuates the closing member, especially at the diaphragm of the inlet opening, whereby the actuation element penetrates at least partially into the diaphragm during the regulation procedure. The hydraulically effective cross section of the diaphragm is essentially determined by the length of the diaphragm, by the diameter of the diaphragm and by the diameter of the part of the actuation element that penetrates into the diaphragm.
In an attempt to attain an optimized flow in the valve part, especially within the range of low temperatures, that is to say, at higher viscosities of the hydraulic fluid, and in order to obtain lower flow resistances, the proportional pressure control valve described in DE 100 34 959 A1 has an optimized configuration of the feed geometry that determines the flow; the length-to-diameter ratio of the diaphragm is selected to be smaller than 2.0 whereby this diaphragm that determines the flow is especially arranged in the admission opening of the valve. As a result, this valve exhibits fewer flow losses, particularly in the case of high oil viscosities, that is to say, at low temperatures; higher flow rates and shorter response times of the valve are achieved, so that this proportional pressure control valve permits better dynamic values.
A specific proportional pressure control valve having a magnet part and a valve part is described herein, whereby the valve part is provided with an inlet opening for the inlet volume flow, with a first discharge opening for the filling volume flow and with a second discharge opening for the tank volume flow, and having a ball seat, a flat seat provided with an opening, a closing member to control the flow rate through the opening in the flat seat and having a stream deflector arranged between the ball seat and the flat seat.
In this control valve the inflow opening for the inflow volume flow is configured at the front end of the valve part facing away from the magnet part and coaxially to the valve part; it is also provided that the discharge opening for the filling volume flow for the coupling to the side wall of the valve part is configured radially to the longitudinal axis of the valve part in such a way that fluid particles flowing from the inflow opening to the discharge opening are subject to a deflection of 90° at the maximum, and that the axial distance of the stream deflector from the ball seat as well as the diameter, the wall thickness and the shape of the stream deflector are all selected in such a manner that, after the fluid particles flow through the ball seat, they flow to and through the stream deflector and are subject to a deflection of less than 30°.
In automatic transmissions, especially in automatic transmissions of automobiles, primarily hydrodynamic converters are employed as the starting element. Particularly when the transmission oil is cold, the energy requirement of the converter is very high, as a result of which the starting behavior of the vehicle is adversely affected. By the same token, the response of the gear shifting elements in the minus temperature range is likewise delayed, which is also detrimental.